Titanium nitride (TiN) is a technologically important transition metal nitride. Hoffman, Polyhedron, 13, 1169 (1994). It is a better electrical conductor than is titanium metal and its optical properties resemble those of gold. Toth, Transition Metal Carbides and Nitrides, J. L. Margrave, ed., vol. 7, Academic Press, New York (1971). Titanium nitride is also harder than all elemental metals and sapphire and almost as hard as diamond, having a melting point of about 3000.degree. C. Additionally, TiN is a low temperature superconductor.
TiN films have many potential applications because of their unique combination of properties. Fix et al., Chem. Mater., 5, 614 (1993). They are used, for example, as wear-resistant, friction-reducing coatings on machine tools and as gold-colored decorative coatings. Their optical properties also make them useful as wavelength selective transparent films, and in particular as solar control coatings on windows in warm weather climates. In microelectric devices, TiN films can be used a low resistance contacts and as diffusion barriers in interconnect metallization schemes.
Inorganic thin films such as TiN are commonly prepared by chemical vapor deposition (CVD). In CVD, a heat decomposable volatile compound (often an organometallic compound), or "precursor", is contacted with a substrate which has been heated to a temperature above the decomposition temperature of the compound. A coating forms on the substrate which may be a metal, metal mixture or alloy, ceramic, metal compound or mixture thereof, depending on the choice of precursor and reaction conditions. Optionally, a volatile reactant gas is employed alone or as a part of the carrier gas to adjust the composition of the final coating. The desirable characteristics of CVD as a thin film formation method include its ability to produce a thin film with good step coverage on a substrate having projections, the ability to readily control the composition of the thin film, and the ability to form a thin film without contamination of, or damage to, the substrate.
However, known CVD processes for manufacturing TiN films suffer many limitations, primarily due to the precursors employed. For example, although it is feasible to carry out CVD employing metalorganic precursors (e.g., dialkylamino-derivatives of titanium [Ti(NR.sub.2).sub.4 ]) to produce TiN films, the carbon content of the resulting TiN film is typically unacceptably high. This problem can be overcome with the use of ammonia in the carrier gas, but this in turn creates problems with gas phase prereactions, with the consequence that the resulting films have poor conformality. Therefore, a need exists for an improved titanium precursor to be used in a CVD process for manufacturing TiN films.